'Data storm' blamed for nuclear plant shutdown

Malfunctioning control device causes fatal spike in traffic

The US House of Representative's Committee on Homeland Security called this week for the Nuclear Regulatory Commission (NRC) to further investigate the cause of excessive network traffic that shut down an Alabama nuclear plant.

During the incident, which happened last August at Unit 3 of the Browns Ferry nuclear power plant, operators manually shut down the reactor after two water recirculation pumps failed. The recirculation pumps control the flow of water through the reactor, and thus the power output of boiling-water reactors (BWRs) like Browns Ferry Unit 3. An investigation into the failure found that the controllers for the pumps locked up following a spike in data traffic - referred to as a "data storm" in the NRC notice - on the power plant's internal control system network. The deluge of data was apparently caused by a separate malfunctioning control device, known as a programmable logic controller (PLC).

In a letter dated 14 May but released to the public on Friday, the Committee on Homeland Security and the Subcommittee on Emerging Threats, Cybersecurity, and Science and Technology asked the chairman of the US Nuclear Regulatory Commission to continue to investigate the incident.

"Conversations between the Homeland Security Committee staff and the NRC representatives suggest that it is possible that this incident could have come from outside the plant," committee chairman Bennie G Thompson (D-Miss.) and subcommittee chairman James R Langevin (D-RI) stated in the letter.

"Unless and until the cause of the excessive network load can be explained, there is no way for either the licensee (power company) or the NRC to know that this was not an external distributed denial-of-service attack."

The August 2006 incident is the latest network threat to affect the nation's power utilities. In January 2003, the Slammer worm disrupted systems of Ohio's Davis-Besse nuclear power plant, but did not pose a safety risk because the plant had been offline since the prior year. However, the incident did prompt a notice from the NRC warning all power plant operators to take such risks into account.

In August 2003, nearly 50 million homes in the northeastern US and neighbouring Canadian provinces suffered from a loss of power after early warning systems failed to work properly, allowing a local outage to cascade across several power grids. A number of factors contributed to the failure, including a bug in a common energy management system and the MSBlast, or Blaster, worm which quickly spread among systems running Microsoft Windows, eventually claiming more than 25 million systems.